The present invention relates to a process for producing a pneumatic tire using a thermoplastic film for an inner liner of the tire which lightens the weight of the tire, without detracting from the retention of air in the tire and reduces a defect rate of the tire and improves the working efficiency during the production of tire.
Reduction of fuel consumption is one of the major technical issues in automobiles. As one of the means for this issue, strong demands have been made for reduction of the weight of pneumatic tires. In this regard, an inner liner layer or other air permeation preventive layer comprised of a halogenated butyl rubber or other rubber having low air permeability is conventionally provided at the inner surface of the pneumatic tire to hold the air pressure in the tire constant. However, a halogenated butyl rubber has a large hysteresis loss, and therefore, after vulcanization of the tire, when rippling is caused in the rubber of the inner surface of the carcass layer and the inner liner layer in the spaces between the carcass cords, the inner liner layer deforms along with deformation of the carcass layer. Thus, there is the problem of an increase in the rolling resistance. Therefore, in general, a rubber sheet called a xe2x80x9ctie rubberxe2x80x9d having a small hysteresis loss has been inserted between the inner liner layer (e.g., halogenated butyl rubber) and rubber of the inner surface of the carcass layer for joining the both layers. Accordingly, in addition to the thickness of the inner liner layer of the halogenated butyl rubber, the thickness of the tie rubber is added and the overall layer becomes a thickness of more than 1 mm (1,000 xcexcm). As a result, this has become a factor increasing the weight of the final tire.
Techniques have been proposed for using various materials in place of the butyl rubber or other low air permeability rubber as an air permeation preventive layer, such as the inner liner layer, of a pneumatic tire. For example, Japanese Unexamined Patent Publication (Kokai) No. 6-40207 proposes the formation of a thin film from an air permeation preventive layer at the inside of the tire by laminating a low air permeability layer comprised of a polyvinylidene chloride film or ethylenevinyl alcohol copolymer film and an adhesive layer comprised of a polyolefinic film, aliphatic polyamide film, or polyurethane film and laminating that thin film on the inner surface of a green tire comprised of unvulcanized rubber so that the adhesive layer contacts the carcass layer, then vulcanizing and molding the green tire. By using this multilayer film for the air permeation preventive layer, it is possible to reduce the thickness of the air permeation preventive layer from the past and possible to reduce the weight of the tire without detracting from the retention of the air pressure.
However, while a pneumatic tire using such a thermoplastic film as disclosed in Japanese Unexamined Patent Publication (Kokai) No. 6-40207 for the inner liner is superior in performance, it has problems in terms of the working efficiency and manufacturing cost and also problems in the occurrence of wrinkles, blistering, etc. at the time of adhesion of the thermoplastic film which has resulted in defective tires. Further, one method of adhering the thermoplastic film is to first manufacture the green tire, then adhere a strip of film to the inner surface or wrap the strip of film and carcass together around the molding drum and then inflate them. In these methods, however, when the adhesive strength at the splice portion of the film is poor, the splice portion (i.e., joined portion) will open up (splice opening) at the time of vulcanization of the tire or the work will be troublesome when manufacturing the green tire and therefore the work efficiency will be poor.
Accordingly, the object of the present invention is to provide a process for producing a pneumatic tire which eliminates the problems in a pneumatic tire using the above thermoplastic film as the air permeation preventive layer of the tire, coats a tackifier-adhesive at the splice portion of the film and/or the joining surfaces of the film and carcass to eliminate the problem of splice opening at the time of tire production, whereby the working efficiency is improved.
In accordance with the present invention, there is provided a process for producing a pneumatic tire using, as an air permeation preventive layer, a strip-shaped or cylindrical-shaped single-layer or multiple-layer thermoplastic film, comprising:
applying, to at least a part of the joining portion of the thermoplastic film or tire member facing the thermoplastic film, a tackifier-adhesive composition containing a polymer component having an absolute value of the difference of the critical surface tension with the rubber component of the tire member and the polymer component of the surface layer of the thermoplastic film of not more than 6 mN/m, respectively.